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Deep and abyssal layer decadal temperature trends from the mid‐1980s to the mid‐2010s are mapped globally using Deep Argo and historical ship‐based Conductivity‐Temperature‐Depth (CTD) instrument data. Abyssal warming trends are widespread, with the strongest warming observed around Antarctic Bottom Water (AABW) formation regions. The warming strength follows deep western boundary currents transporting abyssal waters north and decreases with distance from Antarctica. Abyssal cooling trends are found in the North Atlantic and eastern South Atlantic, regions primarily ventilated by North Atlantic Deep Water (NADW). Deep warming trends are prominent in the Southern Ocean south of about 50°S, the Greenland‐Iceland‐Norwegian (GIN) Seas and the western subpolar North Atlantic, with cooling in the eastern subpolar North Atlantic and the subtropical and tropical western North Atlantic. Globally integrated decadal heat content trends of 21.6 (±6.5) TW in the deep and 12.9 (±1.8) TW in the abyssal layer are more certain than previous estimates. Plain Language Summary: Even the deepest waters in the ocean, which sink to the abyss around Antarctica after being cooled and made saltier by heat exchange with the atmosphere and sea ice formation, have been shown to be warming around much of the globe in recent decades. The net warming rate below 2000‐m depth accounts for about 10% of total ocean heat uptake, but uncertainties in prior estimates have been about half the size of the signal owing to sparse sampling in the deep ocean. However, new observations from Deep Argo floats, capable of profiling to the ocean floor in most locations, have improved that situation in some regions. Here we analyze these new observations together with historical observations collected from ships since the 1970s to map decadal ocean temperature trends around the globe. As a result, we use more historical data than previous estimates. We refine the local patterns of warming and cooling in the waters deeper than 2,000 m. We confirm the amplitude of the net warming below 2,000 m estimated in previous studies, and extend the time covered by those estimates. The increased data coverage substantially reduces the uncertainty of the net warming estimate. Key Points: Analysis of Deep Argo float and historical ship‐based CTD data reveal global patterns in deep and abyssal layer decadal temperature trendsHigh resolution maps reveal spreading of abyssal warming from Antarctica and cooling from the North Atlantic on sub‐basin spatial scalesGlobally integrated decadal heat content trends are 21.6 (±6.5) TW in the deep and 12.9 (±1.8) TW in the abyssal layer [ABSTRACT FROM AUTHOR]

Using 9 years of full‐depth profiles from 55 Deep Argo floats in the Southwest Pacific Basin collected between 2014 and 2023, we find consistent warm anomalies compared to a long‐term climatology below 2,000 m ranging between 11 ± 2 to 34 ± 2 m°C, most pronounced between 3,500 and 5,000 m. Over this period, a cooling trend is found between 2,000 and 4,000 m and a significant warming trend below 4,000 m with a maximum rate of 4.1 ± 0.31 m°C yr−1 near 5,000 m, with a possible acceleration over the second half of the period. The integrated Steric Sea Level expansion below 2,000 m was 7.9 ± 1 mm compared to the climatology with a trend of 1.3 ± 1.6 mm dec−1 over the Deep Argo era, contributing significantly to the local sea level budget. We assess the ability to close a full Sea Level Budget, further demonstrating the value of a full‐depth Argo array. Plain Language Summary: Cold, dense waters formed near polar regions in both hemispheres, sink to great depths and fill‐up the majority of the world's deep ocean. Compilation of sparse observations of temperature from global ship‐based surveys at roughly 10‐year intervals worldwide have shown that sequestration of excess atmospheric heat into the deep ocean has caused these waters to warm steadily since the 1990's into the Present. Not only does this warming have implications for changes in large scale ocean circulation, but is also associated with warming‐induced sea level rise. Using a new data set collected between 2014 and 2023 from 55 freely drifting robotic floats (Deep Argo) which gather crucial bimonthly temperature and salinity data between the surface ocean and the ocean floor, we find the greatest warming trend at a depth of 5,000 m of 4 ± 0.3 m°C yr−1 and an associated sea level rise rate below 2,000 m of 1.3 ± 1.6 mm dec−1. Deep Argo data being collected in ocean basins worldwide are crucial in providing high resolution data of the warming deep ocean and its implications on global sea level, ocean mixing and large‐scale ocean circulation. Key Points: Nine years of Deep Argo data in the S.W. Pacific reveals continued warming in the abyss while the mid‐depths cooledWaters below 4,000 m show an accelerated warming trend with a maximum overall warming rate of 4.1 ± 0.31 m°C yr−1 at 5,000 mDeep ocean steric expansion contributed 1.3 ± 1.6 mm dec−1 to total the local sea level [ABSTRACT FROM AUTHOR]

Watermass transformation in the Irminger Sea, a key region for the Atlantic Meridional Overturning Circulation, is influenced by atmospheric and oceanic variability. Strong wintertime atmospheric forcing in 2015 resulted in enhanced convection and the densification of the Irminger Sea. Deep convection persisted until 2018, even though winters following 2015 were mild. We show that this behavior can be attributed to an initially slow convergence of buoyancy, followed by more rapid convergence of buoyancy. This two‐stage recovery, in turn, is consistent with restratification driven by baroclinic instability of the Irminger Current (IC), that flows around the basin. The initial, slow restratification resulted from the weak horizontal density gradients created by the widespread 2015 atmospheric heat loss. Faster restratification occurred once the IC recovered. This mechanism explains the delayed recovery of the Irminger Sea following a single extreme winter and has implications for the ventilation and overturning that occurs in the basin. Plain Language Summary: The Irminger Sea, between Greenland and Iceland, is known to be an important driver of variability in the global ocean circulation that regulates global climate. During the 2015 winter, the Irminger Sea experienced widespread cooling and buoyancy loss down to 1,000 m, resulting in deeper wintertime mixing than had been observed in the region for many years. This low buoyancy state and deep wintertime mixing persisted from 2015 to 2018, despite a return to average atmospheric wintertime conditions. Here we study how processes that typically provide summertime buoyancy gain to balance wintertime buoyancy loss contribute to the multi‐year recovery of the region. We characterize the recovery of the interior of the Irminger Sea as having two stages: initially slow recovery, followed by more rapid recovery. Our findings are consistent with earlier studies stating that the main source of buoyancy to the interior is eddies shed from the current flowing around the Irminger Sea. This study shows that the deep mixing that is important for global circulation and climate is influenced by changes in the current around the basin. Key Points: Widespread buoyancy loss across the Irminger interior and Irminger Current (IC) delayed the recovery of the interior from strong cooling in 2015Baroclinic instabilities shed from the IC are the dominant source of buoyancy restratifying the sub‐surface Irminger interiorIt is important to consider changes in the IC when considering drivers of variability in convection, ventilation, and the Atlantic Meridional Overturning Circulation [ABSTRACT FROM AUTHOR]

Oceanic transient tracers, such as chlorofluorocarbons (CFCs) and sulfur‐hexafluoride (SF6), trace the propagation of intermediate‐to‐abyssal water masses in the ocean interior. Their temporal and spatial sparsity, however, has limited their utility in quantifying the global ocean circulation and its decadal variability. The Time‐Correction Method (TCM) presented here is a new approach to leverage the available CFCs and SF6 observations to solve for the Green's functions (GFs) describing the steady‐state transport from the surface to the ocean interior. From the GFs, we reconstruct global tracer concentrations (and associated uncertainties) in the ocean interior at annual resolution (1940–2021). The spatial resolution includes 50 neutral density levels that span the water column along World Ocean Circulation Experiment/Global Ocean Ship‐Based Hydrographic Investigations Program lines. The reconstructed tracer concentrations return a global view of CFCs and SF6 spreading into new regions of the interior ocean, such as the deep north‐western Pacific. For example, they capture the southward spreading and equatorial recirculation of distinct North Atlantic Deep Water components, and the spreading of CFC‐rich Antarctic Bottom Water out of the Southern Ocean and into the North Pacific, East Indian, and West Atlantic. The reconstructed tracer concentrations fit the data in most locations (∼75%), indicating that a steady‐state circulation holds for the most part. Discrepancies between the reconstructed and observed concentrations offer insight into ventilation rate changes on decadal timescales. As an example, we infer decadal changes in Subantartic Mode Water (SAMW) and find an increase in SAMW ventilation from 1992 to 2014, highlighting the skill of the TCM in leveraging the sparse tracer observations. Plain Language Summary: The penetration of chlorofluorocarbons (CFCs) and sulfur‐hexaflouride (SF6) into the oceans represents an opportunity to estimate the ventilation rate of the global ocean more directly than other seawater properties. Properties like temperature and salinity are nearly in balance with the ocean circulation and thus are challenging for finding rates of motion, but CFCs and SF6 are transiently evolving due to a great increase in atmospheric concentrations since 1940. However, the analysis of CFCs and SF6 also poses challenges, as they are observed infrequently and they have not had time to permeate the entire global ocean. Here, we analyze over ∼106 CFC and SF6 observations that have been taken over four decades, permitting the largest fraction to date of the global ocean to be analyzed using these tracers. A Time‐Correction Method is developed to address the temporal sparsity of the observations and an eight‐decade annually resolved picture of CFCs and SF6 evolution is produced. Roughly 75% of the observations can be explained by the large‐scale, statistically steady ocean circulation acting on the anthropogenically driven time varying atmospheric concentration. Key Points: New "time‐correction" method permits an annually resolved global view of CFCs and SF6 over eight decadesSteady‐circulation solution is simultaneously consistent with atmospheric histories and 75% of the ∼106 total CFC and SF6 observationsCFCs and SF6, now detected in most of the global ocean, allow for a synopsis of the interior ocean age, ventilation time, and variability [ABSTRACT FROM AUTHOR]

Serendipitous measurements of deep internal wave signatures are evident in oscillatory variations around the background descent rates reported by one model of Deep Argo float. For the 10,045 profiles analyzed here, the average root‐mean‐square of vertical velocity variances, 〈w′2〉 $\sqrt{\langle {w}^{\prime 2}\rangle }$, from 1,000 m to the seafloor, is 0.0045 m s−1, with a 5%–95% range of 0.0028–0.0067 m s−1. Dominant vertical wavelengths, λz, estimated from the integrals of lagged autocorrelation sequences have an average value of 757 m, with a 5%–95% range of 493–1,108 m. Both 〈w′2〉 $\sqrt{\langle {w}^{\prime 2}\rangle }$ and λz exhibit regional variations among and within some deep ocean basins, with generally larger 〈w′2〉 $\sqrt{\langle {w}^{\prime 2}\rangle }$ and shorter λz in regions of rougher bathymetry or stronger deep currents. These correlations are both expected, since larger 〈w′2〉 $\sqrt{\langle {w}^{\prime 2}\rangle }$ and shorter λz should be found near internal wave generation regions. Plain Language Summary: Ocean density increases with increasing depth, supporting internal waves below the ocean surface. These internal waves are generated near the surface by varying wind forcing such as passing storms and near the bottom by interactions of currents (including tidal) with rough bathymetry (such as seamounts and ridges). They can travel for long distances in both the vertical and the horizontal. When they break, they play important roles in mixing temperature, salinity, and other water properties. Deep Argo is an observing system designed to measure temperature and salinity profiles from the surface to the bottom of the ocean. One model of Deep Argo float serendipitously observes internal wave signals as variations in descent rate data, which it collects primarily for navigation purposes, from the surface to the seafloor. These observations reveal patterns in the magnitudes of these internal wave signals, with stronger internal wave activity near continental rises and mid‐ocean ridges and lower levels over smoother abyssal plains. Also, regions with strong deep flows, such as the Samoan Passage through which bottom water is funneled into the North Pacific, or the region south of the Campbell Plateau through which the Antarctic Circumpolar Current flows, exhibit stronger deep internal wave signatures. Key Points: Descent rate data used for navigation by one deep float model serendipitously reveal vertical velocity signatures of internal wavesDeep internal wave vertical velocities average root mean square variances are ∼0.0045 m s−1 and dominant vertical wavelengths are ∼757 mVertical velocity variances and dominant vertical wavelengths exhibit geographical patterns, varying among and within deep ocean basins [ABSTRACT FROM AUTHOR]

Changes in properties and quantity of Antarctic Bottom Water (AABW) have major implications for the climate system, through sequestration of heat and carbon into, and ventilation of, the abyssal ocean. Yet, it remains one of the most difficult water masses to observe. An array of 12 Deep Argo floats, capable of profiling from the surface to the seafloor and under sea ice, provides a new perspective on AABW in the Australian‐Antarctic Basin. Over 2 years of data from the floats illuminate AABW properties with unprecedented detail, simultaneously sampling AABW at multiple locations, year‐round, throughout the basin. Calibrating each float individually with nearby, quasi‐simultaneous shipboard profiles ensures the highest quality salinity data, with estimated accuracy of ±0.005 or better. Pathways of Ross Sea and Adélie Land Bottom Water (RSBW and ALBW), defined by their unique temperature and salinity characteristics, are mapped along the continental slope from their respective sources. The main pathway of RSBW, identified by its characteristic deep salinity maximum, is inferred to be inshore of the 3,700 m isobath, where it cools and freshens westward along the slope before interacting with ALBW near 140°E. A pulse of very cold and very fresh (nearly −0.6°C, 34.82 g kg−1) ALBW appears in February 2019, highlighting temporal variability on daily scales near its source. Deep Argo has greatly enhanced our view of AABW in the Australian‐Antarctic Basin and will prove to be an essential tool for monitoring future changes in the deep ocean by drastically increasing observations in a cost‐effective way. Plain Language Summary: Antarctic Bottom Water (AABW) is both a crucially important component of Earth's climate, with the capacity to store heat and carbon in the abyssal ocean for centuries, and one of the hardest water masses to monitor. New instruments have been developed to do just that. Deep Argo floats are able to take measurements of temperature and salinity from the surface to seafloor and can continue to profile safely while under winter sea ice. 12 Deep Argo floats were deployed in the Australian‐Antarctic Basin and have been continuously profiling for over two years, producing an unprecedented observational data set of AABW properties. We map out pathways of AABW from two source regions: the Ross Sea and Adélie Land. The Ross Sea Bottom Water tends to flow westward hugging the slope, but there is some leakage into the deeper ocean. Near 140°E, Adélie Land Bottom Water flows down the slope, sometimes in pulses, usually slicing under Ross Sea Bottom Water and through a narrow bathymetric saddle between a seamount and the slope. Deep Argo floats offer a window into the deep ocean, enhancing our understanding of AABW and allowing for continuous monitoring of its variability. Key Points: Deep Argo floats map Antarctic Bottom Water properties year‐round and under‐ice in the Australian‐Antarctic Basin from 2018 to 2020Floats reveal Antarctic Bottom Water (AABW) pathways in unprecedented detail and show some Ross Sea Bottom Water hugs the slope and some descends to the deep oceanPulses of Adélie Land Bottom Water descending the slope interact with Ross Sea and Bottom Water (RSBW) and drive short‐term (∼1 day) variability near 140°E [ABSTRACT FROM AUTHOR]

As the abyssal oceans warm, stratification is also expected to change in response. This change may impact mixing and vertical transport by altering the buoyancy flux, internal wave generation, and turbulent dissipation. In this study, repeated surveys of three hydrographic sections in the Southwest Pacific Basin between the 1990s and 2010s are used to estimate the change in buoyancy frequency N2. We find that below the θ=0.8°C isotherm, N2 is on average reduced by a scaling factor of s=0.88±0.06, a 12% reduction, per decade that intensifies with depth. At Θ=0.63°C, we observe the biggest change: s=0.71±0.07, or a 29% reduction per decade. Within the same period, the magnitude of vertical diffusive heat flux is also reduced by about 0.01Wm−2, although this estimate is sensitive to the choice of estimated diffusivity. Finally, implications of these results for the heat budget and global ocean circulation are qualitatively discussed. Plain Language Summary: The large‐scale circulation of the ocean is primarily driven by density differences. As dense, heavy water sinks, it fills the deep ocean basins and aids in pushing water around the globe, cycling around the world over many centuries. A key location where this happens is around Antarctica. The ice and cold winds cool the water, making it denser. This cooled water sinks, displacing the deep water and pushing it northwards. As Antarctica warms, this water carries the extra heat into the rest of the world, causing the deep ocean to rapidly warm. In the Southwest Pacific Basin, we find that this bottom intensified warming has caused a significant reduction in the stratification of the deepest layer over the past three decades. This change can disrupt the global ocean conveyor belt, impacting the transport of heat, carbon dioxide, nutrients, and other dissolved matter around the world. Key Points: A decadal stratification decrease is estimated from 25 years of repeat hydrography in the abyssal Southwest Pacific BasinThis change is significant below Θ = 0.75°C and intensifies with depth, reaching a 22%–36% decrease by Θ = 0.65°CVertical diffusive heat flux is also reduced during the same time period by ∼0.01 Wm−2/decade [ABSTRACT FROM AUTHOR]

There are two varieties of Antarctic Bottom Water present in the Australian Antarctic Basin (AAB): locally produced Adélie Land Bottom Water (ALBW) and distantly produced Ross Sea Bottom Water (RSBW). Between 2014 and 2018, RSBW has rebounded from a multidecade freshening trend. The return of the salty RSBW to the AAB is revealed by six Deep Argo floats that have occupied the region from January of 2018 to March of 2020. The floats depict a zonal variation in temperature and salinity in the bottom waters of the AAB, driven by the inflow of RSBW. A simple Optimum Multiparameter Analysis based on potential temperature and salinity gives a sense of scale to the composition of the bottom waters, which are nearly 80% of the new, salty RSBW in the south‐east corner of the basin by 2019 and generally less than 40% to the west closer to the ALBW outflow region and the abyssal plain. Plain Language Summary: The dense waters that form along the Antarctic coast and fill the global deep oceans have been warming and freshening over the past three decades. This water is integral to the earth's natural system of temperature regulation. New robotic floats from the Deep Argo program are able to record temperature, salinity, and pressure down to the bottom of the ocean and are capturing variability in the quantity and properties of these dense waters near their formation sites better than ever before. Here we examine data from the first 2 years of float deployments in the Indian sector of the Southern Ocean to quantify the rebound in salinity of dense water from the Ross Sea and study how different varieties of this dense water spread and fill the Australian Antarctic Basin before ultimately flowing out into the Indian and Pacific Oceans. Key Points: A new Deep Argo pilot array improves spatial and temporal resolution of bottom water sampling in the Australian Antarctic BasinThe floats capture the return of high salinity Ross Sea Bottom Water to the region after a period of multi‐decadal fresheningA simple Optimum Multiparameter calculation quantifies the local zonal variation in the new water mass concentrations from 2018 to 2020 [ABSTRACT FROM AUTHOR]

The Southern Ocean (SO) is one of the most energetic regions in the world, where strong air‐sea fluxes, oceanic instabilities, and flow‐topography interactions yield complex dynamics. The Kerguelen Plateau (KP) region in the Indian sector of the SO is a hot spot for these energetic dynamics, which result in large spatiotemporal variability of physical and biogeochemical properties throughout the water column. Data from Argo floats (including biogeochemical) are used to investigate the spatial variability of intermediate and deep water physical and biogeochemical properties. An unsupervised machine learning classification approach is used to organize the float profiles into five SO frontal zones based on their temperature and salinity structure between 300 and 900 m, revealing not only the location of frontal zones and their boundaries but also the variability of water mass properties relative to the zonal mean state. We find that the variability is property dependent and can be more than twice as large as the mean zonal variability in intense eddy fields. In particular, we observe this intense variability in the intermediate and deep waters of the Subtropical Zone; in the Subantarctic Zone just west of and at KP; east of KP in the Polar Frontal Zone, associated with intense eddy variability that enhances deep waters convergence and mixing; and, as the deep waters upwell to the upper 500 m and mix with the surface waters in the southernmost regimes, each property shows a large variability. Plain Language Summary: The Southern Ocean strongly influences the global climate system, by absorbing, storing, and redistributing heat and carbon across the different ocean basins. Thanks to an increasing number of observations from autonomous instruments, called Argo floats, our understanding of this harsh environment has deepened in the last two decades. Here we use a machine learning technique to automatically classify the float measurements and sort them in regimes with similar properties based on their temperature and salinity vertical structure. The classification results are consistent with previous studies but are here used to reveal regions where mixing between different types of waters is likely to be occurring. By sorting the float profiles into regimes, we can diagnose regions with larger variation of properties and highlight the transition of the properties across regimes. Given the increasing volume of observations that instruments like the Argo floats are building, a method such as the technique implemented in this study represents a valuable tool that can help to automatically reveal similarities in dynamical regimes. Key Points: An unsupervised classification technique, applied to temperature and salinity float data, is used to sort the profiles into frontal zonesIn eddy fields the variability of physical and biogeochemical properties is more than twice as large as the mean zonal variabilityThe intense eddy variability drives lateral physical processes that cause the large property variance [ABSTRACT FROM AUTHOR]

Data reported from mid‐2014 to late 2018 by a regional pilot array of Deep Argo floats in the Southwest Pacific Basin are used to estimate regional temperature anomalies from a long‐term climatology as well as regional trends over the 4.4 years of float data as a function of pressure. The data show warm anomalies that increase with increasing pressure from effectively 0 near 2,000 dbar to over 10 (±1) m°C by 4,800 dbar, uncertainties estimated at 5–95%. The 4.4‐year trend estimate shows warming at an average rate of 3 (±1) m°C/year from 5,000 to 5,600 dbar, in the near‐homogeneous layer of cold, dense bottom water of Antarctic origin. These results suggest acceleration of previously reported long‐term warming trends in the abyssal waters in this region. They also demonstrate the ability of Deep Argo to quantify changes in the deep ocean in near real‐time over short periods with high accuracy. Plain Language Summary: The coldest waters that fill much of the deep ocean worldwide originate near Antarctica. Temperature data collected from oceanographic cruises around the world at roughly 10‐year intervals show that these near‐bottom waters have been warming on average since the 1990s, absorbing a substantial amount of heat. Data from an array of robotic profiling Deep Argo floats deployed in the Southwest Pacific Ocean starting in mid‐2014 reveal that near‐bottom waters there have continued to warm over the past 4.4 years. Furthermore, these new data suggest an acceleration of that warming rate. These data show that Deep Argo floats are capable of accurately measuring regional changes in the deep ocean. The ocean is the largest sink of heat on our warming planet. A global array of Deep Argo floats would provide data on how much Earth's climate system is warming and possibly improve predictions of future warming. Key Points: Deep and bottom waters in the Southwest Pacific Basin from 2014 to 2018 are increasingly warmer than climatology with increasing depthThe warm anomaly is statistically different from zero at pressures >2,800 dbar and reaches 11 (±1) m°C by 5,500 dbar (1 m°C = 0.001 °C)Deep Argo floats measure a regional mean warming rate of about 3 (±1) m°C/year from 5,000 to 5,600 dbar and from 2014 to 2018 [ABSTRACT FROM AUTHOR]

Abyssal ocean warming contributed substantially to anthropogenic ocean heat uptake and global sea level rise between 1990 and 2010. In the 2010s, several hydrographic sections crossing the South Pacific Ocean were occupied for a third or fourth time since the 1990s, allowing for an assessment of the decadal variability in the local abyssal ocean properties among the 1990s, 2000s, and 2010s. These observations from three decades reveal steady to accelerated bottom water warming since the 1990s. Strong abyssal (z > 4,000 m) warming of 3.5 (±1.4) m°C/year (m°C = 10−3 °C) is observed in the Ross Sea, directly downstream from bottom water formation sites, with warming rates of 2.5 (±0.4) m°C/year to the east in the Amundsen‐Bellingshausen Basin and 1.3 (±0.2) m°C/year to the north in the Southwest Pacific Basin, all associated with a bottom‐intensified descent of the deepest isotherms. Warming is consistently found across all sections and their occupations within each basin, demonstrating that the abyssal warming is monotonic, basin‐wide, and multidecadal. In addition, bottom water freshening was strongest in the Ross Sea, with smaller amplitude in the Amundsen‐Bellingshausen Basin in the 2000s, but is discernible in portions of the Southwest Pacific Basin by the 2010s. These results indicate that bottom water freshening, stemming from strong freshening of Ross Shelf Waters, is being advected along deep isopycnals and mixed into deep basins, albeit on longer timescales than the dynamically driven, wave‐propagated warming signal. We quantify the contribution of the warming to local sea level and heat budgets. Plain Language Summary: Over 90% of the excess energy gained by Earth's climate system has been absorbed by the oceans, with about 10% found deeper than 2,000 m. The rates and patterns of deep and abyssal (deeper than 4,000 m) ocean warming, while vital for understanding how this heat sink might behave in the future, are poorly known owing to limited data. Here we use highly accurate data collected by ships along oceanic transects with decadal revisits to quantify how much heat and freshwater has entered the South Pacific Ocean between the 1990s and 2010s. We find widespread warming throughout the deep basins there and evidence that the warming rate has accelerated in the 2010s relative to the 1990s. The warming is strongest near Antarctica where the abyssal ocean is ventilated by surface waters that sink to the sea floor and hence become bottom water, but abyssal warming is observed everywhere. In addition, we observe an infusion of freshwater propagating along the pathway of the bottom water as it moves northward from Antarctica. We quantify the deep ocean warming contributions to heat uptake as well as sea level rise through thermal expansion. Key Points: Bottom waters in the South Pacific Ocean have warmed steadily since the 1990s, based on data from multiple repeat oceanographic transectsMaximum warming of 0.04 degrees C/decade is found within the deep Ross Sea, with the signal weakening to the northAntarctic Bottom Water freshening, limited to around Antarctica in previous decades, has reached the Southwest Pacific Basin in the 2010s [ABSTRACT FROM AUTHOR]